1. Field
The present invention relates, in general, to a Positron Emission Tomography (PET)-Magnetic Resonance Imaging (MRI).
2. Description of Related Technology
PET was developed in mid-1975 by M. Ter-Pogossian, M. Phelps, et al. at Washington University in St. Louis, Mo. in the United States through the use of the principle of the coincidence detection of annihilation radiation. Since then, PET has been developed by several commercial companies including CPS-CTI. Recently, the utilization of PET has greatly increased in the form of PET-Computed Tomography (CT) combination imaging devices.
Meanwhile, MRI was developed in 1973 by P. Lauterbur. MRI is similar to CT or PET to some degree, but is different from them in physical principles. Currently, 10,000 or more MRI devices are used in hospitals all over the world. Basically, since such an MRI device is a morphological or anatomical imaging space rather than a functional imaging space, molecular specificity is insufficient. However, an MRI device has higher temporal and anatomical resolution than a PET device. Further, functional MRI (fMRI) to which a function of obtaining functional images is added was developed by S. Ogawa in 1992. As such a function related to functional images is added, an fMRI device has become a device capable of providing the most excellent brain image in the fields of neuroscience.
When an fMRI device was developed and introduced into the world, the entire academic world related to neuroscience enthusiastically accepted such a new device because an fMRI device was from the standpoint of brain images a very striking device. However, as requests for molecular specificity have been made, that enthusiasm did not last long, and thus attention fundamentally reverted once again to PET. As is well known to those skilled in the art, PET has two principal abilities, specifically, the ability to measure the affinity/distribution of metabolism of specific dispositions such as glucose and ganciclovir, and the ability to measure the affinity/distribution of specific neuroreceptors to ligands of neurotransmitters.
As described above, PET and MRI devices have their own peculiar advantages and disadvantages. In more detail, a PET device can provide body tissue-related molecular and functional information in very high contrast. However, since a PET device fundamentally has a low resolution, there is a limitation in providing anatomical information. In contrast, an MRI device can provide detailed anatomical information about body tissues, but has a limitation in providing molecular and functional information, compared to a PET device.
As described above, due to the advantages and disadvantages of PET and MRI devices, Korean Patent No. 10-0842682 discloses a PET-MRI hybrid system devised to combine PET and MRI devices with each other and obtain anatomical information and molecular information alongside each other. This system is configured such that a first scanner and a second scanner are connected to each other through a transport rail, and a table capable of holding an examination target is provided on the transport rail, thus sequentially obtaining a PET image and an MRI image.
However, the above system disclosed in Korean Patent No. 10-0842682 is problematic in that the object transport rail occupies a large amount of space, and time is required to transport an object from the first scanner to the second scanner through the transport rail, and thus it is impossible to simultaneously obtain PET and MRI images.
In order to solve this problem, in the related technical field, International Patent Publication No. WO06/119085 discloses a PET scintillation detection unit having an optical fiber and an MRI-PET combination system using the same, International Patent Publication No. WO06/071922 discloses an integrated PET/MRI imaging system and PET detector for an Avalanche Photodiode (APD) base for use in simultaneous PET/MRI imaging, and International Patent Publication No. WO08/127369 discloses hybrid PET/MR imaging system.
The PET scintillation detection unit having an optical fiber and the MRI-PET combination system using the same, disclosed in International Patent Publication No. WO06/119085, are configured such that the scintillation detection unit of a PET device is installed within an MRI device, thus sequentially obtaining PET images and MRI images.
However, the scheme disclosed in International Patent Publication No. WO06/119085 is configured using a structure in which scintillation crystals and an optical device are connected to each other through an optical fiber, thus deteriorating the performance of PET. Further, this scheme is problematic in that it is difficult to extend a axial FOV of a PET scanner due to the limitation of a space in which the optical fiber is installed.
Hybrid PET/MR imaging system, disclosed in International Patent Publication No. WO08/127369, is configured such that a PET scanner is disposed in the same radio frequency isolation space as MRI.
However, time is required to transport an object from the first scanner to the second scanner through the transport rail, and thus it is impossible to simultaneously obtain PET and MRI images.
The integrated PET/MRI imaging system and PET detector for an APD base for use in simultaneous PET/MRI imaging, disclosed in International Patent Publication No. WO06/071922, is provided to be used for PET/MRI imaging in which an APD-based PET module is integrated, and is configured such that each detector includes an array of scintillation crystals read out by an array of APDs, the APD-based PET module being positioned in the tunnel of an MR scanner. Further, artifact-free images may be captured by an APD-based PET and MRI system that can be used for a high-resolution and cost-effective integrated PET/MRI system.
However, the above scheme disclosed in International Patent Publication No. WO06/071922 is configured using a structure in which a pre-amplifier is located in an MRI bore, and thus a problem arises in that, due to the spatial restrictions of the inside of the MRI bore, a signal amplification circuit must be integrated, and in that a protection device, such as a copper shield for protecting the circuits from the influence of the inherent characteristics of an MRI environment, that is, high magnetic fields and RF signals, is required. Further, there is a fear that the generation of heat by the signal amplification circuit itself and the generation of heat by the copper shield attributable to gradient coils may cause the reduction of the amplification factor of a photo sensor and the deterioration of PET performance with the passage of time, and that the insertion of the signal amplification circuit and the copper shield may result in the deterioration of MRI performance such as by reducing the intensity of a magnetic gradient field and deteriorating sensitivity to MRI images.